intel-iommu: Fix array overflow

Fix possible array overflow:

drivers/pci/intel-iommu.c: In function ¡dmar_get_fault_reason¢:
drivers/pci/intel-iommu.c:753: warning: array subscript is above array bounds
drivers/pci/intel-iommu.c: In function ¡iommu_page_fault¢:
drivers/pci/intel-iommu.c:753: warning: array subscript is above array bounds

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Cc: Mark Gross <mgross@linux.intel.com>
Acked-by: "Keshavamurthy, Anil S" <anil.s.keshavamurthy@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>